Magnetic blowout contact switch



p 1, 1964 L. J. MELHART 3,147,358

MAGNETIC BLOWOUT CONTACT SWITCH Filed March 31, 1960 INVENTOR LEONARD J. MELHART ATTORNEY United States Patent C) 3,147,358 MAGNETEC BLOWOUT CONTACT SWITCH Leonard J. Melhart, 6511 Abbington Drive, Oxon Hill, Md. Filed Mar. 31, 1960, Ser. No. 19,122 1 Claim. (Cl. 200-147) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention is a continuation in part of-application Serial No. 767,998, filed Oct. 17, 1958, now Patent No. 2,936,390, which relates to switches of the magnetohydrodynarnic type and more particularly to a high current, low inductance contact switch.

In prior art contact-making switches, the contacts are separated by the ambient medium, usually air for low current switch arrangements and oil or some other medium for high current switches and the contacts are brought together to close an electrical circuit. In most switch arrangements an electrical arc is produced when the switch contacts make or break contact. tact portions become very hot which causes the contact elements to wear excessively, pit, burn, and sometimes even fuse together. The switch arcing cuts down on the life of the switch, limits the current handling capacity and requires frequent replacement of the entire switch or switch contacts.

The present invention is directed to a contact-making type switch of parallel conductor construction in which an are produced during closing and opening the switch contacts is magnetically forced away from the contact surfaces during operation. During closing or opening the contacts, an arc will jump between the contacts as they approach each other during closing or as they part when they are withdrawn from each other. As the arc is made, a current flows through the lines and this current flow produces a magnetic field which forces the are away from the ends of the switch contacts and thereby the arc will meet with the switch surfaces away from the end contact surface. Thus, any severe burning, pitting, etc., of the switch contacts associated with the electric arcs will take place on those surfaces of the contact elements which never touch each other; consequently the contact surfaces will remain clean and in good electrical contact condition. Such a switch can be opened and closed many times which far exceeds that of the prior art type of contact switches used for currents of the same intensity.

It is therefore, an object of the present invention to provide a long lasting, simple, and inexpensive contact switch.

Another object is to provide a contact making switch in which any high temperature arcing is forced away from the contact area by an inherent magnetic force to prevent any deleterious effect on the contacting surfaces of the switch.

Still another object is to provide a contact-making switch in a parallel conductor arrangement in which insulation and the conductors are protected from an arc produced at the contact switch.

Yet another object is to provide a contact arrangement which is applicable to switches of various types such as relays, contactors, circuit breakers and other types on contact making devices.

Another object is to provide a high current, low inductance contact switch which conforms to parallel conductor geometry suitable for many switch applications.

The exact nature of this invention as Well as other objects and advantages thereof will be readily apparent from Thus the switch conice consideration of the following specification relating to the annexed drawings, in which:

FIG. 1 illustrates a plan view of a one switch arrange ment made in accordance to the invention;

FIGS. 2-7 are modifications or illustrations of the switch arrangement illustrated by FIG. 1.

The transmission line for the switch device of the present invention is made in the form of parallel conductors separated by an insulation. The switch is inserted in one of the transmission lines and is separated from the other transmission line by the insulating material. The contacts of the switch are connected in the line and adapted to be moved into contact with each other to complate the circuit. For the purpose of minimizing inductance, the switch electrodes or contacts can be made as Wide as the transmission lines to uniformly distribute the current flow across the contacts thereby reducing the switch inductance. The switch can be made with a backing transmission line separated from the contacts by an Thus, the switch can be inserted into insulating material. a continuous transmission line with parallel conductors wherein one conductor is connected to the switch backing plate conductor and the contacts of the switch connected to the other transmission line. Also, the backing plate of the switch can be bent around to form a U at the end with the bent around end made as a stationary contact and then a moveable contact will be provided to make contact with the stationary end. Of course, insulation would separate the backing plate from the moveable contact and the stationary end contact formed by the backing plate. Such a switch could be inserted into a power transmission line to provide control of the current from a power supply to a load.

Now referring to the drawings, there is shown by illustration in FIG. 1, a plan view of a switch made in accordance to the present invention. As shown, the switch 10 comprises electrical conductors in the form of transmission plates 11 and 12 made of any suitable electrical conducting material, preferably copper, separated by a sheet of insulating material 13 such as Mylar or any other suitable material that forms a suitable electrical insulator between the transmission lines. Conductor 12 has an open circuit in the transmission line to form an air gap in the conductor. Movable electrode plates or switch contacts 14 and 15 are secured to the transmission line at the open gap and are adapted to be moved toward each other reduce ionization which tends to cause prefiring of any type of switch. Since high temperatures are developed between the electrode prior to electrode contact, the insulation between the backing transmission line 11 must be sufficient to withstand the hot temperatures. As shown the switch is connected with a condenser source 16 and to a load 17 through the switch 10.

In operation, the switch is electrically secured in a transmission line with the contacts separated suflicieutly to prevent prefiring. The condenser is charged and, when ready, the switch contacts are moved together. As the switch contacts approach each other the high voltage will break down the air gap to form a spark or are between the electrodes. The arc will continue until the electrodes come into contact wherein the current will flow directly through the contacts. The spark or arc across the space between, the contacts ionizes the air and produces high temperature, electrically heated air, as well as metallic electrode vapors in the air gap between the contacts. Current flow through the back transmission plate 11 sets up a magnetic field in the air gap between the electrodes, the

magnetic field forces the hot air and metallic vapors away from the insulation and the back plate in a direction which 1s somewhat perpendicular to the back plate. The magnetic field also forces the spark away from the line between the electrodes such that the spark takes an arcuated path such that the arc meets the switch electrodes off the center and to the side thereof. By forcing the are or spark away from the contact portion of the electrodes the point of contact between the two electrodes is kept clean and free of any burns, pits or electrode vapors formed in the gap during contact with a current supply continuously supplied through the switch, the same effect would take place during breaking the contact of the switch wherein the magnetic field about the back plate would force the sparks away from the point of contact of the switch during breaking the contact. Therefore, there is no deleterious effect on the contacting surfaces of the electrodes. The magnetic blow out effect is also to lengthen the are thereby facilitating the extinguishing thereof. Since the magnetic field forces the metallic vapors and gases away from the electrodes neither the insulation nor the electrodes will become plated and subsequently cause a short circuit.

FIG. 2 is a modification of the switch illustrated in FIG. 1. This modification of the switch operates the same as the switch FIG. 1 and forces the spark or are away from the switch electrodes in the same manner. This switch includes back transmission line 11 and transmission line 12 wherein one switch electrode 14 is connected to the end of transmission line 11 and the other electrode 15 is movably connected to the transmission line 12. It is noted that the insulation 13 extends between a portion of electrode 14 and the back plate to separate the contact portion of the electrode from the back plate. The switch as shown in FIG. 2 can be connected in an electrical line to control the current from a supply source to a load by connecting one side of the supply source to transmission line 11 and the other side of the source to the load with a line from the load connected to transmission line 12 of the switch.

Two switch elements of the modification shown in FIG. 2 can be combined as shown in FIG. 3 to provide a double pole switch with a cross piece 18 movable along the insulated portion to make contact with the poles. In connecting such a switch arrangement into an electrical circuit, the back strap of one switch element will be connected to one line and the back strap of the other switch element will be connected to the other line. Thus the current will pass from one stationary contact through the cross bar to the other stationary contact and then through the circuit line to load.

FIG. 4 is a modification of the switch as shown in FIG. 1 in which the transmission lines are continuous and separated by an insulation material. A movable contact 21 and a stationary contact 22 are arranged to be secured in one of the transmission lines to provide a switch element. The movable switch contact is pivoted at 23 and adapted to swing into contact with the stationary contact to complete an electrical circuit. In the event an excessive current is passed through the switch, the magnetic field about the back strap will force the swinging contact open to break the circuit and simultaneously will force any resulting electric arc outwardly from the contacting surfaces of the switch contacts. When the excess current condition has been corrected, the switch can then be closed manually or automatically to complete the electrical circuit. The hot vapors will be driven away from the contacts when the contacts are closed in the same way as described for the switch device of FIG. 1.

FIG. is a top view of still another modification in which is shown in FIG. 6 in side view. This modification comprises a backing transmission line 11 adapted to be connected in one line of a circuit and is separated from two spaced contacts 24 and 25 by an insulating material 13. The spaced electrodes are adapted to be connected into another line of an electrical circuit and there is provided a movable contact 26 which moves into contacting position between the two stationary contacts. The

movable contact completes the circuit between the two stationary contacts. Again the magnetic field set up about the backing transmission line will force the hot gases and vapors away from the contacting surfaces between the stationary contacts and the movable contact member.

FIG. 7 is still another modification shown in simplified form to include two spring loaded contacts 31 and 32 separated by an insulating material 33 to prevent prefiring of the circuit for the switch arrangement. The insulation is removed from between the electrodes and the springs 34 force the electrodes into contact. As the insulating material is withdrawn from between the electrodes, an are or spark will jump around the end of the insulation. The insulating material prevents the spark from hitting the contacting surfaces of the movable contacts. Again the magnetic field produced, forces the spark away from the contacting surfaces as the insulating material is completely removed to permit the two contacts to be forced together by the springs. Of course, the contacts will be separated by the insulating material to break the circuit between the two contacts. While conductors 31 and 32 do not have to be parallel with each other in this arrangement, it can be considered the two longitudinal components of the arc around the insulation are conductors and parallel to each other and so follow the teachings of this invention.

It is generally understood in carrying out the teaching of the present invention that the conductors or transmission lines of the switch arrangements must be made of suitable material and size to carry the loads intended. Also the insulating material separating the transmission lines and the contacts must have sufficient insulating qualities to prevent break down between the transmission line and the contacts.

Minimum inductance in the transmission lines is achieved by keeping the conductors of the switch short, widening them as much as practicable and securing the two conductors close together while keeping the intervening insulation as thin as the over-voltage safety factor permits. This can be readily determined from the formula L=1.3 l0 dl/w in microhenries for the inductance of a parallel plate transmission line of length, 1, width, w, and separated a distance, d, measured in centimeters.

Since the movable contacts are closely related to the backing transmission line and separated therefrom by the insulating material, the backing transmission line acts as a guide or support for the movable contacts. Furthermore, the contact switches of the present invention will have long life without becoming pitted, burnt, eroded, roughened or overheated due to the hot vapors and gases being blown away from the contacts due to the magnetic field around the transmission line closely related to the contacts of the switch. Such switches can be used in a vacuum, in air, or in oil; however, due to the structure and teaching of the present invention the contacts can withstand much greater currents than prior art switches when used in the same environment. For instance it has been determined that such switches can carry a current of over 10 amperes at very high voltages, such as 20 kv.

Obviously many modifications and variations of the resent invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

A magnetic blowout contact switch adapted to be connected to load lines in an electrical circuit, said switch comprising first and second parallel flat plate electrical conductors, said first electrical conductor backing said second electrical conductor, an insulating material, said insulating material separating said first and second electrical conductors and having suflicient insulating qualities to prevent an electrical discharge between said first and second electrical conductors, said first electrical conductor and said insulating material being continuous, said second electrical conductor having an open circuit therein with oppositely disposed ends separated to form an air gap therebetween, first and second electrodes connected to said oppositely disposed ends of said second conductor with a plane through the electrodes parallel to said first plate conductor, a third electrode positioned in the same plane as said first and second electrodes and movable relative thereto to complete an electrical circuit across said open gap.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Great Britain May 15, 

